SPC Jun 18, 2025 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0754 AM CDT Wed Jun 18 2025

Valid 181300Z - 191200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
SOUTHEAST MISSOURI INTO SOUTHERN/EASTERN ILLINOIS...WESTERN
KENTUCKY...INDIANA...WESTERN OHIO...AND SOUTHERN LOWER MICHIGAN...

...SUMMARY...
Severe thunderstorms are expected today from parts of southern
Missouri northeastward to the southern Great Lakes. Scattered to
numerous damaging winds, isolated large hail, and a few tornadoes
all appear possible. Strong to severe thunderstorms may also develop
across parts of the southern Plains, northern Plains/Upper Midwest,
and Mid-Atlantic.

...Mid Mississippi/Ohio Valleys to the Southern Great Lakes...
Embedded within large-scale upper troughing, a well-defined MCV
evident on radar and visible satellite imagery over MO this morning
will quickly advance northeastward today across the mid MS Valley
into the Midwest, and eventually the southern Great Lakes this
evening. This feature will likely aid robust thunderstorm
development across parts of eastern IL into IN and vicinity by late
morning/early afternoon. Sufficient low-level and deep-layer shear
will exist across the Midwest for updraft organization, including
supercells. However, convection may quickly become linear; so, it
remains unclear how long a supercell hail/tornado threat will exist.
Regardless, filtered daytime heating of a rather moist low-level
airmass will aid the development of at least moderate instability
downstream of any convection that develops.

With 40-50 kt of low/mid-level southwesterly flow forecast across
parts of the mid MS Valley into the OH Valley/Midwest and steepening
low-level lapse rates through the day, scattered to perhaps numerous
damaging winds appear likely with organized clusters/bows spreading
east-northeastward across these regions through the afternoon and
early evening. The severe wind threat should extend as far north as
parts of southern Lower MI, along/near a surface front. Some risk
for line-embedded tornadoes may also exist. By mid to late evening,
these clusters should gradually weaken as they continue eastward
into a less unstable environment across the OH Valley. But, they may
still pose some threat for damaging winds for as long as they can
remain surface based.

...Southern Plains to the Mid-South...
Ongoing convection across central OK may continue to pose an
isolated hail/wind threat in the short term this morning, before
eventually weakening as the nocturnal low-level jet aiding this
activity slowly subsides. In the wake of these early-day
thunderstorms, ample daytime heating of a seasonably moist airmass
is anticipated along/south of a convectively reinforced cold front,
with moderate to strong instability expected. The southern Plains
will be on the southern periphery of upper troughing across the
mid/upper MS Valley today, but enhanced mid-level winds should still
be present from parts of OK eastward into AR and the Mid-South.

Multiple bands/clusters should form this afternoon along/south of
the front in a favorable thermodynamic environment given the
continued presence of steep mid-level lapse rates, especially across
OK/TX. While deep-layer shear is not forecast to be overly strong,
it should still be sufficient for updraft organization, including
the potential for a few supercells. Initial development this
afternoon may pose more of a severe hail threat, before clustering
occurs and the risk for severe/damaging winds increases with
eastward/southward extent later in the afternoon and continuing into
the evening.

...Northern Plains/Upper Midwest...
Behind upper troughing over the mid/upper MS Valley, northwesterly
mid-level flow around 25-40 kt should be present today over portions
of the northern Plains and Upper Midwest. Low-level moisture is
expected to remain fairly limited, with surface dewpoints mostly in
the 50s. Even so, steepened low/mid-level lapse rates are
anticipated through the afternoon, along with weak to moderate
instability. While large-scale ascent should remain weak, widely
scattered thunderstorms may still form and spread
east-southeastward, with some threat for isolated severe wind gusts
and marginally severe hail this afternoon and early evening. Modest
deep-layer shear should keep the overall severe threat fairly
isolated/marginal.

...Mid-Atlantic...
Within modestly enhanced mid-level southwesterly flow, an embedded
weak perturbation is forecast move northeastward today from the
southern/central Appalachians across the southern Mid-Atlantic. A
moist low-level airmass in place across this region, with surface
dewpoints generally in the upper 60s to low 70s. Ample daytime
heating will likely foster moderate to locally strong instability
along/east of the Blue Ridge Mountains by mid afternoon. Current
expectations are for thunderstorms to develop initially over the
higher terrain and move eastward in a modest deep-layer shear
environment. Some thunderstorm organization should occur, with
multicells as the main convective mode. This activity may pose some
threat for damaging winds this afternoon and evening until it moves
off the Atlantic Coast or weakens with the loss of daytime heating.

..Gleason/Kerr.. 06/18/2025

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